The human spine, known technically as the vertebral column, is constituted of a plurality of articulating vertebrae, and extending downwards towards fused vertebrae in the sacrum and coccyx. Using standard anatomical terminology, the vertebral column is found in the dorsal aspect of the torso. The articulating vertebrae are separated from adjacent vertebrae on either side by an invertebral disc which forms a cartilaginous joint to allow slight movement of the vertebrae, and further acts to hold the various vertebrae together so as to form the vertebral column.
Each invertebral disc comprises an outer annulus fibrosus, often simply called the annulus, which surrounds and contains the nucleus pulposus which is a jelly-like substance which functions to distribute hydraulic pressure within each invertebral disc under compressive loads. In the event of an invertebral disc defect, such as a prolapsed or herniated disc, the nucleus pulposus is forced out through the defect of the annulus, and may apply pressure to nearby nerves or to the spinal cord. In severe cases the escaping nucleus pulposus may cause chemical irritation of nearby nerve roots. Protrusion of the nucleus pulposus may be variously referred to as a disc bulge, a herniated disc, a ruptured disc or a sequestered disc, depending on the specific diagnosis.
In order to avoid confusion in describing medical devices, certain fixed terminology is utilized. In particular, the term proximal usually means closer to the surgeon, unless otherwise stated, and the word distal usually means further removed from the surgeon, unless otherwise stated. Surgery to repair a defect in the annulus is usually performed from the patient's dorsal side, i.e. from the back, and thus the terms proximal and distal are understood with the surgeon approaching from the patient's back; however this is not meant to be limiting in any way. In the event of surgery performed ventrally, the terms need to be understood in relation to a dorsal operation.
While various schemes for repair of the annulus defects are known, one common solution is a surgical procedure known as discectomy which involves the surgical removal of the herniated disc material. Discectomy is often performed in conjunction with a laminectomy, where a small piece of bone, known as the lamina, is removed from the affected vertebra, allowing the surgeon to better see and access the area of disc herniation.
One problem with the above procedure is that additional nucleus pulposus material may be ejected from the annulus over time by the unsealed defect in the annulus, which is not sealed by the discectomy. Thus, a device and associated procedure is required to seal the annulus defect. Various devices and procedures are known to the prior art, including without limitation, WIPO Patent Publication S/N WO 2010/089717 entitled “Implantable Device for Sealing a Spinal Annular Fissure Tear and Method for Deploying the Same”, the entire contents of which are incorporated herein by reference. One issue not fully addressed by the above subject patent publication, and other devices of the prior art, is the issue of ejection, i.e. the tendency of any device placed in the annulus to be ejected over time responsive to forces developed in the remaining nucleus pulposus material.
Certain improved devices are described in WIPO Patent Publication S/N WO 2012/120509 entitled “Spinal Disc Annulus Closure Device”, the enter contents of which are incorporated herein by reference, based on a tubular format. One of the challenges of such a device is to stand up to strong hydrostatic ejection forces of up to 20 atmospheres while not interfering with a full range of motion of the vertebral column. Unfortunately, such a tubular format experiences difficulty with repeated sagittal flex and extension.
What is desired, and not supplied by the prior art, is a device arranged to: seal the annulus against further release of nucleus pulposus material through the defect; resist ejection from the annulus; allow for a full range of motion of the vertebral column over an expected patient lifetime without fatigue failure; and be easily manipulated to an insertion size.